Analysis Problems Identified Because of its concern about the frequency and potential consequences of occurrences at the Port of Sorel, the Board did a preliminary analysis of the above occurrences. The Board identified the following problems: Shoals reduce the manoeuvring area available and limit vessel manoeuvrability. The tugs available did not provide sufficient assistance under the circumstances. Shoals Material in suspension in the Richelieu River causes silting. Over the years, the accumulated sediment has formed shoals in the estuary and in the St.Lawrence River on both sides of the mouth of the Richelieu River. To assess the gravity of the silting problem, soundings were taken and dredging was done in the area. In the 10years preceding this occurrence, the situation had been monitored regularly by sounding. However, efforts to deal with the silting problem have not produced the results expected. Dredging operations were concentrated alongside the wharfs and rarely included the central portion of the estuary. In the absence of a dredging program covering the entire mouth of the Richelieu River, sedimentation on the shoals will tend to flow toward the dredged areas alongside the wharfs. Silting, therefore, will continue to affect the hydrodynamic behaviour of vessels stopping in this section of the port. Room to Manoeuvre By limiting their dredging operations to the area just off the wharfs that they operate, the berth operators have considerably reduced the manoeuvring zone. As a result, at the mouth of the Richelieu River, the access channel in the St.Lawrence River is divided into two lanes to provide access to the Richelieu River: one lane on the west side leads to berth19; another leads to berths14and15. Only shallow-draught vessels can use the middle of the Richelieu River to reach berths16,17and18. Squat Effect Shoals affect a vessel's hydrodynamic performance. The water that should flow under the hull encounters resistance due to low under-keel clearance. The water flowing under the bow moves faster, creating a low-pressure area. This results in a loss of flotation, causing the vessel to squat by the bow. The mass of water that builds up in front of the vessel increases resistance and shifts the pivot point3 aft. As a result, the steering lever is shorter, and more propeller thrust and/or greater rudder deflection is required to maintain a heading. The manoeuvrability of a vessel in this condition is sometimes unpredictable.4 In this occurrence, the speed of the vessel over the ground plus the speed of the countercurrent, estimated at two and three knots respectively, produced a speed through the water of about five knots during the approach. At this speed, the vessel tended to squat over the shoals. Pilots who execute approaches in this area have often observed this phenomenon. Mariners and pilots use a chart and a worksheet to calculate under-keel clearance as a standard for vessels transiting the confined waters of the St.Lawrence River.5 Marine traffic regulators use this under-keel clearance standard to evaluate the squat effect on vessels. Converging Currents To navigate safely, mariners must have a good knowledge of the local currents and constantly monitor a current's direction and strength. The currents of the Richelieu and St.Lawrence rivers meet in the mouth of the Richelieu. Consequently, a vessel proceeding toward a berth at the entrance to the Richelieu must stem both currents simultaneously. The Richelieu current pushes against the port shoulder, and the St.Lawrence current pushes against the starboard quarter. The combined effect of the two forces applies a yawing moment on the vessel, causing it to swing to starboard. The investigation established that the majority of pilots use the Richelieu River current to induce sideways movement towards the berths. By ordering kicks ahead or slow forward propulsion with the main engine, it is possible to stem the current by maintaining the pivot point in the fore part of the vessel. This ensures that the steering lever is adequate to manoeuvre and control the vessel. However, if the pivot point is allowed to shift further forward, the moments produced by the bow thruster and the forward tug, in relation to the pivot point, will decrease accordingly. However, the vessel must not be positioned too far crosswise of the current. If the angle between the vessel's heading and the current is too great, considerable propeller thrust will be required to turn the vessel back into the current. If the water's resistance (created by the current's striking the shoulder of the vessel) is too great, the main engine will be unable to produce enough thrust to overcome that resistance. Unless a great deal of manoeuvring room is available, the vessel will swing out of control in the wrong direction. Loss of Manoeuvrability The effect of low under-keel clearance can be insidious and violent. If the vessel is placed athwart the current, the swing will be even greater. When this happens, mariners tend to reduce the vessel speed or even stop the main engine to shift the pivot point aft. This shortens the steering lever and the vessel will not answer properly to the wheel. To regain control of the vessel, power must be increased to maintain torque and apply propulsion forward and helm hard-over in the desired direction. However, if in this case the pivot point shifts further aft, the moments produced by the bow thruster and the forward tug in relation to the pivot point will increase accordingly. In this occurrence, the manoeuvres ordered by the pilot did not produce the expected results. Off berth 15, the combined thrust of the bow thruster and the OcanGolf was initially insufficient. The vessel's speed was reduced to complete the drift into the berth. A swing to port was begun but, as the vessel was too far athwart the current, a swing to starboard ensued. Even the full thrust of the vessel's propeller, combined with that of the forward tug and the bow thruster, was not enough for the vessel to stem the current. In other words, the moment produced by the thrust of the vessel's propeller, the bow thruster, and the tug in relation to the pivot point was not enough to overcome the moment produced by the current on the hull. Tug Assistance When berth 19 at Pointe-aux-Pins was rebuilt to accommodate the trans-shipment of steel products, marine traffic increased on the Richelieu River in the Port of Sorel. Of the 313pilotage assignments for marine traffic on the Richelieu in1999, 136were for this maritime terminal. In addition, departures were made by vessels drawing 8.18m on average, the second-highest average. Despite this growth in traffic on the Richelieu, the tug service has remained unchanged in the port. When several pilots experienced unexpected yaw occurrences over the years, they started to make more frequent requests for tugs with higher bollard-pull ratings. This service was provided by tugs from the Port of Montral. Keeping a vessel on heading in a current is difficult without adequate tug assistance. The limited space available in the estuary does not provide sufficient manoeuvring room to regain control of the vessel. For many years, and until quite recently, the OmniSt-Laurent and the OmniRichelieu provided towing services in the Port of Sorel. Even though these conventional tugs and their replacements, whose manoeuvrability and performance were comparable, may be economical to operate, their manoeuvrability and performance is now considered limited. The tugs are slow and, at times, their manoeuvring is restricted when repositioning in relation to a vessel. When made fast to the bow of a vessel, these conventional tugs tend to increase the vessel's headway and push on the ship's side, because they only rarely push at right angles to the hull. In this occurrence, the forward component of the push from the forward tug and the vessel's propeller thrust increased the headway of the FederalFuji and drove it toward the TecamSea. The presence of shoals in the port reduced the under-keel clearance of the vessel and adversely affected the vessel's hydrodynamic behaviour. The manoeuvres ordered by the pilot on the FederalFuji did not produce the expected results. The thrust of the propeller, the bow thruster, and the forward tug was not enough to overcome the effect of the current's pushing against the port shoulder of the FederalFuji. The forward component of the thrust of the forward tug and the vessel's propeller increased the headway of the FederalFuji and drove it toward the TecamSea.Findings as to Causes and Contributing Factors The presence of shoals in the port reduced the under-keel clearance of the vessel and adversely affected the vessel's hydrodynamic behaviour. The manoeuvres ordered by the pilot on the FederalFuji did not produce the expected results. The thrust of the propeller, the bow thruster, and the forward tug was not enough to overcome the effect of the current's pushing against the port shoulder of the FederalFuji. The forward component of the thrust of the forward tug and the vessel's propeller increased the headway of the FederalFuji and drove it toward the TecamSea. Ongoing silting at the mouth of the Richelieu River creates shoals. The existing dredging program does not fully cover the river mouth. Conventional tugs with a low bollard pull are unable to maintain a vessel on heading when the vessel is athwart the current.Findings as to Risks Ongoing silting at the mouth of the Richelieu River creates shoals. The existing dredging program does not fully cover the river mouth. Conventional tugs with a low bollard pull are unable to maintain a vessel on heading when the vessel is athwart the current. Safety Action Action Taken On 21 June 2000, representatives of the Laurentian Pilotage Authority, Fednav International Limited, and the Corporation of Mid-St.Lawrence River Pilots met to review the operating procedures for the Port of Sorel. Solutions under consideration include dredging the mouth of the Richelieu River off berths14, 15, and19, soundings, and using a tug more powerful than LaPrairie. In June 2001, the Ocean Group took delivery of the 360 azimuth-drive 3040kW tug H-9901 to operate permanently in the Port of Sorel. This tug offered greater directional stability and, since its arrival, the number of reportable occurrences decreased substantially. However, in August2001, it was sold and replaced by the variable pitch, twin screw, 4829kW OceanHercule. According to the Navigable Waters Protection Division of Fisheries and Oceans Canada, only one dredging operation at the mouth of the Richelieu River has been approved since this accident, namely a dredging operation to a depth of 7.4m carried out in September2002 off section No.14. A dredging project is to be submitted to the Quebec provincial department of environment by the Socit des parcs industriels Sorel-Tracy. The sea bottom at the mouth of the Richelieu River would be dredged to a depth of 8.5m off the docks and to a depth of 11.0m in the centre of the river. It is expected this project could become a reality in the fall of2003.